Good design is infinitely better than any amount of work you spent. If your design was good, then those kids with their cool tutorials and SOC editing GUIs still can't beat you if it's good to begin with. If it was utter garbage, of course they're going to beat you out. It'll just happen faster if they are better equipped.
The only way you can keep ahead of the curve is if you keep doing things that are cool and interesting, as well as just doing very quality work. I would be absolutely thrilled if someone created a single player pack of levels that outdoes Mystic Realm, because that means I'd get the privilege of playing it. Being the top dog means nothing to me, I just want to see quality new stuff. If I'm taken off the top because of it, then that means I guess I'd better get to work to try and compete if I want to keep my throne. A competition to see who could create the best content would be totally win-win for everyone, because that means everyone would get to play cool new stuff.
If being the number one person is your goal in life, you are completely doomed to failure, and I don't see why you're here if your goal is to get to the top. It's almost impossible to get there, and when someone does, no one can stay there, no matter who they are. However, if your goal is to make cool stuff so everyone can enjoy it, no matter what happens, you're a winner. Stop worrying about the new people coming in with better tools, because you've got both those tools and experience, something that no newbie will ever have when they start. Experience is more important than any tool, tutorial, or gimmick, because experience is what makes good content possible.